What is Registers? Types of Registers

Register :-

Register are used to quickly accept, store, and transfer data and instructions that are being used immediately by the CPU, there are various types of Registers those are used for various purpose. Among of the some Mostly used Registers named as AC or Accumulator, Data Register or DR, the AR or Address Register, program counter (PC), Memory Data Register (MDR) ,Index register,Memory Buffer Register.

These Registers are used for performing the various Operations. While we are working on the System then these Registers are used by the CPU for Performing the Operations. When We Gives Some Input to the System then the Input will be Stored into the Registers and When the System will gives us the Results after Processing then the Result will also be from the Registers. So that they are used by the CPU for Processing the Data which is given by the User. Registers Perform:-

 

1)    Fetch: The Fetch Operation is used for taking the instructions those are given by the user and the Instructions those are stored into the Main Memory will be fetch by using Registers.

 

2)    Decode: The Decode Operation is used for interpreting the Instructions means the Instructions are decoded means the CPU will find out which Operation is to be performed on the Instructions.

 

3)    Execute: The Execute Operation is performed by the CPU. And Results those are produced by the CPU are then Stored into the Memory and after that they are displayed on the user Screen.

 

                                                Types of Registers are as Followings:                                                                                      

MAR stand for Memory Address Register

 

This register holds the memory addresses of data and instructions. This register is used to access data and instructions from memory during the execution phase of an instruction. Suppose CPU wants to store some data in the memory or to read the data from the memory. It places the address of the-required memory location in the MAR.

 

Program Counter

 

The program counter (PC), commonly called the instruction pointer (IP) in Intel x86 microprocessors, and sometimes called the instruction address register, or just part of the instruction sequencer in some computers, is a processor register

It is a 16 bit special function register in the 8085 microprocessor. It keeps track of the the next memory address of the instruction that is to be executed once the execution of the current instruction is completed. In other words, it holds the address of the memory location of the next instruction when the current instruction is executed by the microprocessor.

 

Accumulator Register

This Register is used for storing the Results those are produced by the System. When the CPU will generate Some Results after the Processing then all the Results will be Stored into the AC Register.

 

Memory Data Register (MDR)

MDR is the register of a computer's control unit that contains the data to be stored in the computer storage (e.g. RAM), or the data after a fetch from the computer storage. It acts like a buffer and holds anything that is copied from the memory ready for the processor to use it. MDR hold the information before it goes to the decoder.

 

MDR which contains the data to be written into or readout of the addressed location. For example, to retrieve the contents of cell 123, we would load the value 123 (in binary, of course) into the MAR and perform a fetch operation. When the operation is done, a copy of the contents of cell 123 would be in the MDR. To store the value 98 into cell 4, we load a 4 into the MAR and a 98 into the MDR and perform a store. When the operation is completed the contents of cell 4 will have been set to 98, by discarding whatever was there previously.

 

The MDR is a two-way register. When data is fetched from memory and placed into the MDR, it is written to in one direction. When there is a write instruction, the data to be written is placed into the MDR from another CPU register, which then puts the data into memory.

 

The Memory Data Register is half of a minimal interface between a micro program and computer storage, the other half is a memory address register.

 

Index Register

A hardware element which holds a number that can be added to (or, in some cases, subtracted from) the address portion of a computer instruction to form an effective address. Also known as base register. An index register in a computer's CPU is a processor register used for modifying operand addresses during the run of a program.

 

Memory Buffer Register

MBR stand for Memory Buffer Register. This register holds the contents of data or instruction read from, or written in memory. It means that this register is used to store data/instruction coming from the memory or going to the memory.

 

Data Register

A register used in microcomputers to temporarily store data being transmitted to or from a peripheral device.




Chapter : Memory & Input/Output Unit

• Computer Fundamental 

Input and Output Devices

The devices which are used to input the data and the programs in the computer are known as "Input Devices". or  Input device can read data and convert them to a form that a computer can use. Output Device can produce the final product of machine processing into a form usable by humans. It provides man to machine communication. Some of the I/O devices are explained below:

 

(1) Keyboard : Keyboard is used in the input phase of a computer-based information system. Keyboard is most common input device is used today. The data and instructions are input by typing on the keyboard. The message typed on the keyboard reaches the memory unit of a computer. It’s connected to a computer via a cable. Apart from alphabet and numeral keys, it has other function keys for performing different functions.

 

(2) Mouse : It’s a pointing device. The mouse is rolled over the mouse pad, which in turn controls the movement of the cursor in the screen. We can click, double click or drag the mouse. Most of the mouse’s have a ball beneath them, which rotates when the mouse in moved. The ball has 2 wheels of the sides, which in turn mousse with the movement of the ball. The sensor notifies the speed of its movements to the computer, which in turn moves the cursor/pointer on the screen.

 

(3) Scanner : Scanners are used to enter information directly in to the computers memory. This device works like a Xerox machine. The scanner converts any type of printed or written information including photographs into digital pulses, which can be manipulated by the computer.

 

(4) Track Ball : Track ball is similar to the upside- down design of the mouse. The user moves the ball directly, while the device itself remains stationary. The user spins the ball in various directions to effect the screen movements.

(5) Light Pen : This is an input device which is used to draw lines or figures on a computer screen. It’s touched to the CRT screen where it can detect raster on the screen as it passes.

 

(6) Optical Character Rader : It’s a device which detects alpha numeric characters printed or written on a paper. The text which is to be scanned is illuminated by a low frequency light source. The light is absorbed by the dark areas but reflected from the bright areas. The reflected light is received by the photocells.

 

(7) Bar Code Reader : This device reads bar codes and coverts them into electric pulses to be processed by a computer. A bar code is nothing but data coded in form of light and dark bars.

 

(8) Voice Input Systems : This devices converts spoken words to M/C language form. A micro phone is used to convert human speech into electric signals. The signal pattern is then transmitted to a computer when it’s compared to a dictionary of patterns that have been previously placed in a storage unit of computer. When a close match is found, the word is recognized.

 

(9) Plotter : Plotter is an O/P device that is used to produce graphical O/P on papers. It uses single color or multi color pens to draw pictures as blue print etc.

 

(10) Digital Camera : It converts graphics directly into digital form. It looks like an ordinary camera, but no film is used therein, instead a CCD (changed coupled Divide) Electronic chip in used. When light falls, on the chip though the lens, it converts light waves into electrical waves.

 Chapter : Memory & Input/Output Unit

• Computer Fundamental

What is FPU (math coprocessor)?

FPU stands for floating point unit, a small chip built into some computers. Sometimes referred to as a math coprocessor or a math chip, an FPU can calculate complex mathematical problems and various graphic tasks much faster than the "general purpose" CPU (central processing unit) found in all computers. It's called a floating point unit because its speed really shows when calculating equations involving numbers having decimal portions, such as 67.9345x 0.00345. 



Chapter : Introduction to Computer

• Computer Fundamental 

What is Density?

Density reflects the closeness of data on a disk: the closer the data is, the denser a disk is said to be. Of course, when data is placed closer together (more densely), a disk can store more data. Floppy disks, which are magnetic data storage devices, come in two commonly used sizes: 3.5-inch and 5.25-inch. Both sizes are available in two densities: double- density and high-density. Inside a floppy disk is a thin piece of film with a magnetic coating. The magnetic coating is where data is stored. Density refers to the amount of magnetic particles in the coating.

Regardless of the size of the particle, it can only store one piece of data. A high-density disk has smaller magnetic particles, which allows more particles to fit on a disk, and makes it possible for the disk to store more data. A double-density disk has larger particles that are not so tightly packed; therefore, it holds less data. (A hard disk, by the way, uses a different type of magnetic material that is much denser than the magnetic material used on any floppy disk. This allows a hard disk to hold a lot more data.)

A 3.5-inch double-density disk can hold 720 kilobytes of data. A 3.5-inch high-density disk can hold 1.44 megabytes of data. A 3.5-inch disk can only be used in a 3.5-inch floppy disk drive. A 5.25-inch double-density disk can hold 360 kilobytes of data, and a 5.25-inch high-density disk can hold 1.2 megabytes. A 5.25-inch disk can only be used in a 5.25-inch floppy drive. It is also important to know what type of density the floppy drive is made to handle. Most new disk drives are high-capacity drives, and can handle both high-density and double-density disks. However, older drives were low-capacity and can only handle double-density disks. 

Chapter : Introduction to Computer

• Computer Fundamental

What is Dual Floppy Drive?

A computer with a dual floppy drive has two slots in which to insert a floppy disk. Although several years ago this meant you simply had two of the same kind of floppy drives so you could work from two different disks, it now usually means that one of the drives will take a 3.5-inch high-density floppy disk, and the other will take a 5.25-inch floppy disk.

Chapter : Introduction to Computer

• Computer Fundamental 

What is Docking Station?

A docking station is a unit that attaches to a laptop or notebook computer, either directly or by cable, providing the laptop with more hardware. This arrangement increases the laptop's capabilities almost to that of a standardized desktop computer. A docking station typically includes standard expansion slots, as well as additional ports (sockets) for connecting a printer, modem, keyboard, etc. So if you have a laptop computer and a docking station, you can take your laptop with you wherever you go, accepting its limitations as a laptop. Then when you come home or go back to the office, you can connect your laptop to the docking station (with some units this is like inserting a giant video tape into a VCR). Then your laptop virtually turns into a regular desktop computer, complete with large monitor, large hard disk, more RAM, etc

Chapter : Introduction to Computer

• Computer Fundamental 

What is Bus Snooping?

Bus Snooping: A mechanism for maintaining CACHE COHERENCY in MULTIPROCESSOR computers, under which each cpu's cache-control logic watches the external memory bus, looking for reads or writes made by other processors (that is, it 'snoops' on their transactions). Whenever such a transaction is detected, the cache logic enquires whether a copy of the target address exists in its own cache, and if so either writes that line back to memory or declares it invalid.

Chapter : Introduction to Computer

• Computer Fundamental 

What is backside bus?

A second PROCESSOR BUS built into high-performance microprocessors, such as the PENTIUM II and later, used to connect the processor to its LEVEL 2 CACHE memory so that the latter does not have to share the bandwidth of the ordinary I/O bus with main memory accesses.

Chapter : Introduction to Computer

• Computer Fundamental

What is Dumb Terminal?

A terminal consists of a screen and keyboard which allow you to interact with a multi-user computer; the computer itself is often located in another room or even a different building. A dumb terminal, which is the most common type of terminal, has no computing capabilities of its own. You enter commands on the terminal's keyboard to tell the computer what to do, and the computer sends messages back to you on the terminal's screen. The computer does all the work (of running programs, for example), with no help from the dumb terminal.

Chapter : Introduction to Computer

• Computer Fundamental

What is Bus Master?

Bus Master: Any device within a computer that is capable of taking control of the BUS and initiating data transfers with the memory and PERIPHERALS (which are slave devices and can only respond passively to access attempts). In simple systems the CPU is the only bus master, but in others such as the PC I BUS, there may be multiple masters: for example it is common for a SCSI disk controller to be granted bus master status so that it can transfer data to and from memory without CPU involvement.

Chapter : Introduction to Computer

• Computer Fundamental

What is Parallel Computer?

A computer with multiple processors that can all be run simultaneously on parts of the same problem to reduce the solution time. The term is nowadays mostly reserved for those MASSIVELY PARALLEL computers with hundreds or thousands of processors that are used in science and engineering to tackle enormous computational problems.There are two fundamental divisions in parallel computer architecture. The first is between those architectures in which each processor has it own memory space and communicates with others by MESSAGE PASSING, and those architectures in which all the processors communicate through a shared memory (SHARED-MEMORY MULTIPROCESSORS). The increasing number of high-end PCs and servers that contain more than one processor fall into this latter category.

The other fundamental division is between those computer architectures in which each processor executes the same program on a different data item (SINGLE-INSTRUCTION MULTIPLE-DATA or SIMD)and those in which each processor executes a different program (MIMD or multiple-instruction multiple-data). Within these subdivisions, the processors can be connected together in many different ways (their TOPOLOGY) which profoundly affect the efficiency of communication between them. 

 Chapter : Introduction to Computer

•  Computer Fundamental

  

What is (floppy disk, high density) FDHD?

FDHD stands for floppy disk, high density and refers to the floppy disk drive in current Macintosh models. This drive can read and write single sided disks (400K), double-sided disks (800K), and high-density disks 0.2 megabytes). It can also understand 3.5" Dos-formatted disks from IBM PCs and Apple II machines. An FDHD is also known as a SuperDrive.

 Chapter : Introduction to Computer

•  Computer Fundamental

What is bus width?

If you think of the computer's bus as being a freeway that carries data, then it is easy to visualize the bus width as the number of lanes on this freeway. Naturally, the more lanes available, the more data that can be carried at any given moment. Bus widths are generally designated in multiples of eight; a 32-bit bus width has the capability to carry four times the information of an 8-bit bus in the same amount of time.

  Chapter : Introduction to Computer

• Computer Fundamental

What is Bus Locking?

Bus Locking: A type of BUS architecture in which some particularly bandwidth-hungry device, for example a GRAPHICS PROCESSOR, is permitted to keep control of a computer's bus for many successive cycles to the exclusion of other devices. It was employed in some early Apple MACINTOSH systems to improve graphics throughput, but would be frowned on in today's highly multitasking, multiprocessor environments.

Chapter : Introduction to Computer

• Computer Fundamental

What is PDA (personal digital assistant)?

PDA stands for personal digital assistant, a term for a new breed of handheld computers. PDAs are supposed to combine the power and flexibility of a real computer with the convenience of those little electronic organizers- the kind made by Sharp and Casio-that let you keep track of your names and addresses and to-do items.A PDA can run much more complex software than an electronic organizer, and you're not stuck with the built in software-you can buy separate programs to customize the PDA to your specific tasks. With many PDAs you can use a stylus to write on the little screen. The PDA most people are talking about is the Newton, made by Apple, but many other companies are planning their own versions.

Chapter : Introduction to Computer

• Computer Fundamental

What is Analytical Engine?

 The Analytical Engine, designed by Charles Babbage between 1833 and 1846, anticipated many features of electronic computing devices invented in the 1940s and 1950s. Although mechanical in all its operations, the Analytical Engine could carry out calculations of arbitrary complexity under the control of punched cards. Conditional branching was possible, and Babbage had prepared test programs that included elaborate calculations based on nested loop structures. In a beautiful anticipation of twentieth-century thinking, Babbage showed that, given sufficient time, any finite calculation could be carried out by the Analytical Engine.

 Chapter : Introduction to Computer

•  Computer Fundamental

What is expansion bus or Microcomputer Buses?

On a microcomputer, the bus is usually called anexpansion busbecause its design determines the degree to which the minimum configuration of the system can be expanded with regard to memory, processing speed, graphics capability, and peripheral support. The expansion bus is the collection of wires, paths, connectors, and controllers responsible for distributing the data and instructions from the microprocessor to the peripheral expansion cards.Slotsconnected to the bus provide places to plug those cards in, and the bus then provides a mechanism for communicating with them.In modern designs the expansion bus is not normally the same bus that the CPU uses to access MAIN MEMORY, as the contention this would cause could slow the whole system down. Expansion cards may also be allowed to use DIRECT MEMORY ACCESS to avoid involving the CPU in most of their memory operations.

Examples of expansion buses include the ISA BUS and PCI BUS in the PC world, the VMEBUS for UNIX systems and the NUBUS for the Apple MACINTOSH.

Chapter : Introduction to Computer

• Computer Fundamental 

Bad Sector

                       What is bad sector?

A disk has two sides (a top and a bottom). Each side of the disk has tracks or concentric rings on the surface. Each ring is divided like a pie into equal wedges, or sectors, which are the smallest units of storage space on the disk. If one of these units is damaged or flawed, it is considered a bad sector and cannot be used.

If there was already data in that sector when it got damaged, chances are slim that you can recover that data unless you have the specialized hardware and software necessary for that sort of operation. Almost all hard disks are born with bad sectors, so don't freak out if your software utility reports them. Other bad sectors should not start appearing, though, after you start using the disk.

 Chapter : Introduction to Computer

•  Computer Fundamental

Bus Speed

                      What is Bus Speed? 

Bus Speed: The rate at which a computer's PROCESSOR BUS can transmit data, which is a crucial determinant of its overall performance. The bus speed of most personal computers remained at 33 MHz for a decade, only recently being increased to 100 MHz, and technologies such as the two-level processor CACHE, DIRECT MEMORY ACCESS or the Accelerated GRAPHICS PORT can be seen as ways to surmount this restriction by bypassing the processor bus.

Chapter : Introduction to Computer

• Computer Fundamental